These days, overhead projectors and slide projectors are widely used when speakers present their materials in conferences or the like. Video projectors and motion film projectors employing liquid crystal displays are also becoming popular for home applications. Typically, these projectors optically modulate light from light sources via transparent liquid crystal display panels into image-forming light and emit this image-forming light through optical systems such as lenses, thereby projecting the emitted image-forming light onto screens.
For example, a front projector which can form color images on a screen includes an illumination optical system which separates a light beam emitted from a light source into light components for red (R), green (G), and blue (B) and combines each light component on a predetermined optical path; a liquid crystal display panel (light valve) which optically modulates each light component for red, green, and blue that is separated by the illumination optical system; and a light-combining unit which combines the light components for red, green and blue that are optically modulated by the liquid crystal display panel. The front projector magnifies the color image composed by the light-combining unit to project it onto a screen via a projection lens.
Furthermore, projectors that spatially modulate each light component for red, green and blue using a narrow-band, three-primary-color light source as a light source, and a grating light valve (GLV) in place of the liquid crystal display panel are also being developed these days.
Incidentally, the above-described projectors employ projection screens to project images. These projection screens are broadly divided into a transmissive type in which light is emitted from behind the screen to project an image onto the screen, and a reflective type in which light is projected from the front onto the screen to reflect an image. With either type, bright and high-contrast images are necessary for the screen to provide excellent visibility.
However, unlike self-luminescent displays and rear projectors, the front projector described above exhibits a problem in that it cannot reduce reflection of extraneous light with, e.g., an ND filter, whereby enhancement of the luminous contrast on the screen is difficult.
To address this problem, in Japanese Patent No. 2889153, as shown in FIG. 10, a transparent layer 102 is formed on a diffusion layer 101 and protrusions 103 are formed on the surface of the transparent layer 102. Opaque layers 104 are formed by applying black-coating only on the side walls of the protrusions 103. The provision of these opaque layers 104 lowers the black level, leading to an enhancement in brightness and contrast. However, pattern formation and partial coating require time and work. Furthermore, although screens should preferably be flexible for easy storage, this screen has no flexibility. Moreover, Japanese Patent No. 3103802 discloses an example of a flexible screen as shown in FIG. 11. With this screen, all of a supporting member 201, a reflective layer 202, a light absorption layer 203, and a diffusion layer 204 composing the screen are flexible, thereby imparting flexibility to the screen itself. However, the light absorption layer is disposed closer to the surface of the screen than the reflective layer so that the light absorption layer absorbs even the light intended to be reflected, resulting in a lower white level.
The projectors described above reflect projected light that has been subjected to image processing onto the screen, and the image contrast greatly depends on the brightness of the surroundings. Simply increasing the reflectance of the screen allows not only the projected light but also the extraneous light to be well reflected, resulting in deterioration of the perceived image. Hence, it is difficult to obtain a clear image in a bright environment.
The present invention aims to solve the aforementioned problems and it is an object of the present invention to provide a clear image regardless of the brightness of the environment where a projection screen is used.